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Plain-language information for patients

What is a heart attack?

A heart attack (myocardial infarction) happens when the blood supply to part of the heart muscle is suddenly blocked, usually by a clot. The muscle is starved of oxygen and starts to be damaged, so treatment must not be delayed.

Call 999 immediately if you suspect a heart attack

Typical symptoms are chest pain or tightness that may spread to the arm, neck, jaw or back, often with sweating, breathlessness, nausea or a feeling of dread. Symptoms can be milder or different — especially in women, older people and those with diabetes — so do not wait to be sure.

Call 999 straight away. While waiting, sit and rest; if advised and not allergic, an adult can chew a 300 mg aspirin.

What happens next

In hospital an ECG and a blood test (troponin) help confirm the diagnosis. The main treatment for a major heart attack is to reopen the blocked artery quickly, usually with an emergency procedure (primary PCI).

Afterwards, medicines and cardiac rehabilitation reduce the risk of another event.

Common questions

What is the difference between a heart attack and cardiac arrest?

A heart attack is a circulation problem (a blocked artery) and the person is usually conscious. A cardiac arrest is when the heart stops pumping and the person collapses and is unresponsive — start CPR and call 999.

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This page is general information, not personal medical advice, and does not replace a consultation with a qualified health professional. If you are worried about your health, please speak to your GP, pharmacist, or another clinician. Last reviewed 2026-06-09.